There exist specialized pneumatic couplings that are commonly used in automotive repair shops to connect pneumatic tools and fixtures such as air driven impact drivers, air chucks and the like to an air line. In such couplings a male portion of the coupling, which commonly consists of a grooved nipple attached to a tool, is releasably connected to a self-sealing female coupling attached to an air line. Tools and fixtures, which are expensive, are commonly stolen by simply disconnecting the coupling. Although it is possible to accomplish such thefts by cutting the air line, this is not done because of the noise resulting from high pressure air escaping from a cut air line. Since the mechanics who work in such shops very often supply their own tools, such thefts result in expensive personal, monetary losses. The present invention therefore, seeks to prevent the theft of a tool or fixture attached to an air line by a coupling by providing a combination lock to a pneumatic, self-sealing female coupling.